1. Field of the invention
The present invention relates to a V-shaped belt (hereinafter referred to as V belt) type continuously variable transmission.
2. Description of the Prior Art
In general, a V belt type continuously variable transmission contains an input pulley composed of a pair of half pulleys mounted on an input pulley shaft to move axially toward and away from each other, an output pulley composed of a pair of half pulleys mounted on an output pulley shaft to move axially toward and away from each other, and a V belt which frictionally engages the pulleys to transmit the rotation from the input pulley shaft to the output pulley shaft to vary the rotational speed continuously.
The means to transmit the rotation between both pulley shafts depends upon the V belt member only in the V belt type continuously variable transmission which is actually used at present. In such a construction, there are several defects as follows;
Firstly the allowable transmission capacity is limited by the V belt becomes strength so that the improvement of the transmission capacity and the compaction of the construction are obstructed.
Secondly when the V belt stuck into the groove between half pulleys of the output pulley shaft because the vehicle stopped suddenly and its wheels and the output pulley shaft connected to them are brought to stop, power transmitting becomes impossible. Or, the drive ratio is made to the higher position so that the restart becomes difficult or the acceleration is not accomplished satisfactorily due to weak drive power.
If the movable input half pulley is forced to be moved by large power to change the drive ratio in the state when the V belt stuck, the pulley or V belt is damaged.
When the V belt is cut away, it goes without saying that the vehicle becomes impossible to operate.
To overcome those defects, countermeasures have been proposes to include a sub power transmitting path which is provided in addition to the power transmitting path with the V belt so that either one of them selectively transmits its output power through a hydraulic clutch or the like to the wheels in compliance with the drive ratio.
The above proposed construction, however, still has the following problems.
Firstly switching of the paths is accompanied by shock.
Secondly, two clutches are required at least to switch respective output from each power transmitting path so that the construction becomes large size with great weight and high production cost, and controlling of the system tends to be complicated.
Thirdly, condition of sliding malfunction or sticking of V belt is apt to be irregular so that judgment of the condition is difficult and effective recovery action is not performed.
Furthermore, in a V belt type continuously variable transmission of this kind, as shown in FIG. 16, one input half pulley B of a pair of input half pulleys B, C mounted on a input pulley shaft A is made to move axially along the input pulley shaft and the position of the input half pulley B is controlled by a half pulley position control D operated through an actuator not shown. The half pulley position control D contains an outer slider E to be rotatably operated by the actuator and an inner slider F to be engaged through screw with the outer slider E which supports the rear end of the input movable half pulley B. Consequently, when the outer slider E moves toward and away along the input pulley shaft through the actuator, the input movable half pulley B is moved to be controlled in its position. In such conventional V belt type continuously variable transmission, however, the axial load due to the V belt H during operation is directly added to the power transmitting members of the actuator such as a bearing G, an outer slider E, etc. so that these members, for instance the bearing G, are damaged or great operating power is necessary for the actuator.